1. Field of the Invention
The present invention relates to an electrically driven apparatus having a motor for driving a mirror in a single-lens reflex camera, and more precisely, it relates to an apparatus (previewer) for detecting or confirming a focal depth.
2. Description of Related Art
In recent cameras, particularly in an expensive single-lens reflex camera, a mirror is driven by a motor. The mirror driving apparatus has a mother plate provided on the side face of a mirror box to support a gear train which is driven by the motor and a mirror box mechanism which is driven by the rotation of the gear train. The mirror box mechanism usually performs successive operations of stepping down of an aperture of a lens, an upward movement of the mirror, a release of a mechanical engagement of an electromagnetic shutter, a downward movement of the mirror after the shutter operates, and a release of the stop-down of the lens aperture. Accordingly, in the mirror driving mechanism, it is necessary to engage the gear train supported on the side face of the mirror box with a drive shaft of the motor. However, in the conventional apparatus, the drive shaft of the motor extends in parallel with the side face of the mirror accordingly a worm-wheel mechanism or a bevel gear mechanism must be provided between the drive shaft of the motor and the gear train. However, the worm-wheel mechanism and the bevel gear mechanism are very expensive and have a low driving force transmission efficiency. Furthermore, it is difficult to preform the motor integral with the mirror box, resulting in the difficulty of realizing a united mirror box incorporating the motor therein. Namely, upon assembly, the gear on the mirror box side must be precisely engaged with the gear of the drive shaft of the motor.
A single-lens reflex camera having a motor provided on the bottom of the mirror box is also known. However, in such a recent AF single-lens reflex camera, an AF distance measuring module is located on the bottom of the mirror box. Accordingly, the motor cannot be located on the bottom of the mirror box.
On the other hand, in a conventional previewer of a single-lens reflex camera, the stop-down operation is mechanically effected by a manual lever. However, since the diaphragm is usually biased in an open position with a relatively large force, a photographer must operate the manual lever with a large force against the biasing force making it very difficult for a photographer to maintain the stop-down position.
A camera having a holding device which maintains the stop-down position is also known. However, in this type of camera, reset and set operations, which are troublesome, are necessary. If the previewer is actuated by an electrical drive mechanism of the mirror, a photographer's burden could be decreased.